蒙特卡罗模拟四极阱中原子的参变激发

在中性原子的磁囚禁实验中,磁阱线圈的电流噪声会激发磁阱中的原子运动,势必对原子团的温度和寿命产生不可忽视的影响。对于非简谐阱,这种激发具有能量选择特性,它又取决于电流噪声的频谱分布。选择了实验中常用的四极阱为研究对象,用直接模拟蒙特卡罗方法来模拟四极阱中原子运动的参变激发现象,得到了原子温度与原子数损失随激发频率的变化关系,并进一步计算了两个共振峰处原子温度随调制时间和调制深度的变化曲线。此外,还研究了弹性碰撞速率对参变激发过程中原子温度上升的影响。这些结果对四极阱参变激发的实验有较好的参考价值。

In the experiment of magnetic trapping of neutral atoms, the current noise in the coils will excite the atomic motion, which influences greatly the temperature and the lifetime of the trapped atoms. For anharmonic trap, this excitation has energy-selective characters, and depends on the frequency spectrum of the current noise. The quadrupole trap is chosen as a research object, which is widely used in experiment. The direct simulation Monte Carlo method is used to model the phenomenon of parametric excitation of the atomic motion in the quadrupole trap, and the excitation frequency dependences of the temperature and the trap loss of the atoms are studied. The temperature of the atom cloud is calculated further as the functions of the modulation time and the modulation depth at the two resonant peaks. Furthermore, the influences of the elastic collision rate on the temperature increase of the atom cloud in the process of parametric excitation are also addressed. These results are valuable reference for the experiment of parametric excitation in a quadrupole trap.